The contraction of open wounds has only recently been found to be a function of contractile fibroblasts, known as myofibroblasts. This proposal describes studies of the ultrastructural characteristics of myofibroblasts both in experimental models which have specific clinical analogs and in human surgical specimens. Studies will be made of granulatifg wounds, contracting wounds covered by full and split thickness skin grafts, and slowly contracting wounds caused either by radiation injury or adriamycin injury to the skin. Sequential biopsies of these tissues will allow investigation of the life cycle of the myofibroblasts, seeking to answer the questions of the origin of these cells and their ultimate fate. Specific details of the intracellular contractile mechanism will also be studied, using specialized electron microscopic preparation techniques. By learning in which pathologic wound conditions contractile cells occur, and detailing their life cycles, it may be possible to gain a better understanding of how problem wounds may be modified by therapeutic measures.